Merge remote-tracking branch 'remotes/armbru/tags/pull-error-2015-06-09' into staging

Error reporting patches

# gpg: Signature made Tue Jun  9 06:42:15 2015 BST using RSA key ID EB918653
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>"
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>"

* remotes/armbru/tags/pull-error-2015-06-09:
  vhost-user: Improve -netdev/netdev_add/-net/... error reporting
  QemuOpts: Convert qemu_opt_foreach() to Error
  QemuOpts: Drop qemu_opt_foreach() parameter abort_on_failure
  blkdebug: Simplify passing of Error through qemu_opts_foreach()
  QemuOpts: Convert qemu_opts_foreach() to Error
  QemuOpts: Drop qemu_opts_foreach() parameter abort_on_failure
  vl: Fail right after first bad -object
  vl: Print -device help at most once
  vl: Report failure to sandbox at most once

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>